Active night vision thermal control system using wavelength-temperature characteristic of light source

ABSTRACT

A thermal control system ( 11 ) for a light source ( 46 ) of a vision system ( 10 ) includes a heater ( 63 ) that is thermally coupled to the light source ( 46 ). A thermal sensor ( 60 ) is thermally coupled to the light source ( 46 ) and generates a temperature signal. A controller ( 50 ) is coupled to the heater ( 63 ) and to the thermal sensor ( 60 ). The controller ( 50 ) operates the heater ( 63 ) when the temperature signal is below a maximum temperature limit. The minimum and maximum temperature limits are obtained from the light-source wavelength-temperature characteristic.

CROSS REFERENCE TO RELATED APPLICATION(S)

The present application is a divisional of U.S. patent application Ser.No. 11/164,550, filed Nov. 29, 2005, which is a Continuation-In-Part ofU.S. patent application Ser. No. 10/604,376, filed Jul. 15, 2003, nowU.S. Pat. No. 6,969,855.

STATEMENT

The specification contains no new matter.

TECHNICAL FIELD

The present invention relates to night vision systems, and moreparticularly, to a system and method of thermally controlling operatingrange of a light source of an active night vision system using thewavelength-temperature characteristic of the light source.

BACKGROUND OF THE INVENTION

Night vision systems allow a vehicle occupant to better see objectsduring relatively low visible light level conditions, such as atnighttime. Night vision systems typically are classified as eitherpassive night vision systems or active night vision systems. Passivesystems simply detect ambient infrared light emitted from objects withina particular environment. Active systems utilize a light source toilluminate a target area and subsequently detect infrared lightreflected off objects within that area.

Passive systems typically use far-infrared cameras characterized by lowresolution and a relatively narrow field-of-view. Such cameras must belocated on the vehicle exterior in order to acquire requisite infraredenergy in the operating environment. Externally mounted cameras cannegatively affect vehicle styling. Far-infrared cameras are also costlyto manufacture and generate images that have poor contrast, which can bedifficult to interpret.

Active systems provide improved resolution and image clarity overpassive systems. Active systems utilize laser or incandescent lightsources to generate an illumination beam having near infrared lightenergy, and charged coupled devices (CCD) orcomplementary-metal-oxide-semiconductor (CMOS) cameras to detectreflected infrared light. Active systems commonly deploy a light sourceexternal to the vehicle so as to transmit a significant amount of lightenergy and provide a bright scene for imaging.

Diode lasers are preferred over incandescent light sources for severalreasons. Incandescent light sources are not monochromatic like diodelasers, but instead emit energy across a large spectrum, which must befiltered to prevent glare onto oncoming vehicles. Filtering asignificant portion of energy from a bulb is expensive, energyinefficient, and generates undesired thermal energy. Also, filterpositioning is limited in incandescent applications, since the filtermust be located proximate an associated light source. As well, multipleincandescent sources are often required to provide requisiteillumination, thus increasing complexity and costs.

Exterior mounted light sources or cameras are undesirable due to risk ofdamage during a vehicle collision. Night vision components arerelatively expensive and, as a result, protection of the components isdesired. Also, exterior mounted light sources and cameras aresusceptible to theft. Additionally, external mounting of sources andcameras can limit and compromise vehicle design and styling, can beesthetically displeasing, and can increase exposure of the devices todust and debris. Exposure to dust and debris negatively effectsperformance of the sources and cameras. When the sources and cameras aredirty, light transmission and reception can be substantially reduced,and compromise system performance.

Exterior mounted semiconductor illumination sources have additionalassociated disadvantages. A significant disadvantage is controlling thewavelength of the illumination beam. Night vision systems have apreferred wavelength operating range. When a night vision system isoperated outside this range the received illumination decreases,negatively affecting image quality of the night vision system. The diodelaser emission wavelength is sensitive to change in temperature, suchthat the wavelength of a diode laser output shifts approximately 0.25 nmfor every one-degree Celsius temperature change. Since externaltemperatures vary considerably, it is difficult to control thetemperature of a diode laser. Also, when mounted externally, a risk ofexposure to water exists, which can render the laser inoperable. Sealingand housing problems due to thermal energy management may also arisewhen weatherproofing diode lasers.

Furthermore, in designing a vehicle exterior, the external light sourcemay have to be customized to satisfy styling requirements. Thus it isdifficult to achieve commonality for light sources between differentvehicles. Designing different light sources for different vehicles iscostly.

In the parent application, U.S. patent application Ser. No. 10/604,376,a bandpass filter is used to detect a light reflected from objects inthe scene. The bandpass filter is used to remove most of the light fromoncoming headlights which prevents the camera image from blooming andenables the system to see into the lights of the opposing vehicles. Thesystem uses a filter having a full-width-at-half-maximum (FWHM) of about13 nm. This value is relatively high and still allows a substantialamount of light from oncoming headlights to be introduced into thesystem. The value of the filter is chosen to accommodate themanufacturing tolerances between the various light sources. It wouldtherefore be desirable to provide an improved active night vision systemthat reduces the filter FWHM value substantially below that of 13 nm toallow even more light to be filtered from oncoming headlights.

SUMMARY OF THE INVENTION

The present invention provides a thermal control system for asemiconductor light source of an active night vision system of avehicle. A thermal control system for a light source of a vision systemincludes a heater that is thermally coupled to the light source. Athermal sensor is thermally coupled to the light source and generates atemperature signal. A controller is coupled to the heater and to thethermal sensor. The controller operates the heater when the temperaturesignal is below a maximum temperature limit. The temperature limits aredetermined as a function of the wavelength temperature curve of thelight source.

One of several advantages of the present invention is that it provides athermal system for a light source of a vision system that maintains adesired operating range of the light source. In so doing, the presentinvention accurately maintains desired illumination wavelength of thelight source thus allowing a narrower filter to be used. The narrowerfilter allows greater light filtering, and in comparison to a systemthat uses a wide filter, minimizes or eliminates bloom in regions of theimage near the headlamps of oncoming cars.

Another advantage of the present invention is that it is thermallyconfigured as to efficiently adjust temperature of the light source.

Furthermore, the present invention is designed such that it may beutilized within an interior cabin of a vehicle. Interior cabin useallows for easier temperature control of the light source and minimizesrisk of exposure to water or condensation on the light source.

Yet another advantage of the present invention is that it provides athermal control system that is compact in design and may be located invarious locations within an interior cabin of a vehicle.

The present invention itself, together with further objects andattendant advantages, will be best understood by reference to thefollowing detailed description, taken in conjunction with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of an active night vision systemutilizing a thermal control system in accordance with an embodiment ofthe present invention.

FIG. 2 is a side perspective and block diagrammatic view of the activenight vision system utilizing the thermal control system in accordancewith an embodiment of the present invention.

FIG. 3 is a block diagrammatic view of an illuminator system utilizingthe thermal control system in accordance with an embodiment of thepresent invention.

FIG. 4 is a block diagrammatic view of a receiver system in accordancewith an embodiment of the present invention.

FIG. 5 is a plot of transmission versus wavelength of a filter and lightsource.

FIG. 6 is a logic flow diagram illustrating a method of thermallycontrolling operating range of a light source in accordance with anembodiment of the present invention.

FIG. 7 is a block diagrammatic view of a tunable filter apparatusaccording to another embodiment of the invention.

DETAILED DESCRIPTION

In the following figures the same reference numerals will be used torefer to the same components. While the present invention is describedwith respect to a system and method of thermally controlling operatingrange of a light source of an active night vision system, the presentinvention may be applied in various applications where near infraredimaging is desired, such as in adaptive cruise control applications,collision avoidance and countermeasure systems, and in image processingsystems. The present invention may be applied during daytime hours or atnight. The present invention may be applied in various types and stylesof vehicles as well as in non-vehicle applications.

Also, although the present invention is described with respect to anillumination system that is configured to be mounted within an overheadconsole of a vehicle, the present invention may be applied to lightsources within or exterior to an interior cabin of a vehicle, as well asto other light sources.

In the following description, various operating parameters andcomponents are described for one constructed embodiment. These specificparameters and components are included as examples and are not meant tobe limiting.

Additionally, in the following description the term “near infraredlight” refers to light having wavelengths within the infrared lightspectrum (750 nm to 1000 nm) and light having wavelengths near or justoutside of the infrared light spectrum. The term also includes at leastthe spectrum of light output by the particular laser diode sourcedisclosed herein.

Referring now to FIGS. 1 and 2, front and side perspective views of anactive night vision system 10 utilizing a thermal control system 11 inaccordance with an embodiment of the present invention are shown. Thevision system 10 is configured for an interior passenger cabin 12 of avehicle 14. The vision system 10 includes an illumination system 16 anda receiver system 18. The illumination system 16 generates anillumination beam 20 having a beam pattern 22, which is directed towardsa target area 24 that is forward of the vehicle 14. Portions of theillumination beam 20 are reflected off objects (not shown) within thetarget area 24 and are received by the receiver system 18 having areceiver system controller 228. The receiver system 18 indicates tovehicle occupants, via an indicator 26, detection of the objects inresponse to reflected portions of the illumination beam 20. The thermalcontrol system 11 thermally controls the operating range of theillumination system 16.

The illumination system 16 is configured to be mounted within anoverhead console 30 above a rearview mirror 32, and the receiver system18 is configured to be mounted forward of a driver seat 34 on adashboard 36. Of course, the illumination system 16 and receiver system18 may be mounted in other locations around windshield 38 as well asother window and non-window locations within the vehicle 14.

Referring also to FIG. 3, a block diagrammatic view of the illuminatorsystem 16 utilizing the thermal control system 11 in accordance with anembodiment of the present invention is shown. The illumination system 16includes an illuminator assembly 40 and the thermal control system 11.

The illuminator assembly 40 includes a light source assembly 42 thatgenerates light, which may be emitted from the assembly 42 in the formof an illumination beam, such as beam 20. Light generated from the lightassembly 42 is directed through an optic assembly 44 where it iscollimated to generate the illumination pattern 22. The illuminationbeam 20 is emitted from the light assembly 42 and passed through thewindshield 38. The light assembly 42 includes a light source 46 that iscontained within a light source housing 48. The light source 46 alsoreceives an illumination signal from the illumination controller 50. Theintensity of the illumination beam 20 is controlled by the illuminationsignal.

The light source 46 may be of various type and style. In one embodimentof the present invention the light source 46 is a near infrared diodelaser, having desired monochromatic and illumination characteristics.The diode laser may, for example, be a Single Stripe Diode Laser, ModelNo. S-81-3000-C-200-H manufactured by Coherent, Inc. of Santa Clara,Calif. The light source has a wavelength-temperature characteristic orcurve. The characteristic or curve may be provided from the light sourcemanufacturer. The characteristic or curve is measured for eachindividual light source since this curve has a tendency to vary from onelight source to the next due to manufacturing tolerances and the like.

The optical system 44 includes the light assembly 42, a light coupler52, and a beam-forming optic 54. Light from the light source 46,represented by arrow 55, is emitted towards and is reflected by thelight coupler 52 to the optic 54, where it is again reflected towardsand through the windshield 38. The light coupler 52 and the optic 54 maybe contained within a component alignment maintaining module or housing(not shown). The optical system 44 may also include a series of lightemitting diodes (LEDs) 56 or the like for performing color mitigationand for adjusting perceived color of the illumination beam 20 as it isemitted from the illuminator assembly 16. Light emitted by the LEDs 56is represented by arrows 57.

The light coupler 52 may be in the form of a mirror, as shown, a seriesof mirrors, a fiber optic cable, or other reflective or lighttransporting device known in the art. In the embodiment as described,light is emitted from the light source 46 in the form of an ellipticallyshaped beam with a spread angle of approximately 20-50°, which is thenreflected at approximately a 90° angle by the light coupler 52 to enterthe optic 54. Although, the present invention is described with respectto the incorporated use of a light coupler 52, the present invention maybe modified to have direct emission of light between the light source 46and the optic 54, without use of a light coupler 52.

Although, the optic 54 may be preferably a thin sheet optical element,it may be in some other form. Continuing from the above-describedembodiment, the optic 54 expands and reflects the light generated by thelight source 46 at approximately a 90° angle to direct the light forwardof the vehicle 14. Light from the light source 46 enters and isreflected and/or collimated by the optic 54, and is then reflected andemitted through the windshield 38. Also, although a single optic isshown, additional optics may be incorporated within the illuminationsystem 16 to form a desired beam pattern onto a target external from thevehicle 14.

The optic 54 may be formed of plastic, acrylic, or of some other similarmaterial known in the art. The optic 54 can utilize the principle oftotal internal reflection (TIR) and form the desired beam pattern withseries of stepped facets; An example of a suitable optical element isdisclosed in U.S. patent application Ser. No. 09/688,982 entitled“Thin-Sheet Collimation Optics For Diode Laser Illumination Systems ForUse In Night-Vision And Exterior Lighting Applications”.

The thermal control system 11 includes a thermal sensor 60, a coolingassembly 61 that has a cooling device 62, a heater 63, and thecontroller 50. The cooling device 62 and the heater 63 are in operativeresponse to the thermal sensor 60, via the controller 50, as isdescribed in further detail below. The cooling device 62 aids in thermalenergy transfer away from the light source 46. The heater 63 providesand transfers thermal energy into the light source 46. The coolingdevice 62 and the heater 63 operate to maintain temperature of the lightsource 46 within a pre-determined temperature range. For example, adiode laser may have a desired temperature operating range ofapproximately 40°-55° C., where 40° C. may be considered a maximumtemperature limit and 55° C. may be considered a minimum temperaturelimit. These limits may vary as is further described in more detailbelow. A heat sink 64 is provided and allows thermal energy transferbetween the light assembly 42 and the cooling assembly 61. Thermalenergy is absorbed by the heat sink 64 from the light assembly 42 and isradiated into the cooling assembly 61.

The thermal sensor 60 is thermally coupled to and senses the temperatureof the light source 46 and may be in the form of a thermistor or othertemperature-sensing device known in the art. The thermal sensor 60 maybe part of the light assembly 42 and located within the light housing48, as shown, or may be separate from the light assembly 42 or thehousing 48. The temperature sensor 60 may be coupled to the heat sink todetermine the temperature of the light source.

The cooling device 62 is in thermal communication with the heat sink 64,via an air sleeve 66. The thermal system 11 circulates air around aperimeter 68 of the heat sink 64 and disperses thermal energy from theheat sink 64 into an air gap 70 between a headliner 72 and a roof 74 ofthe vehicle 14, thereby cooling the heat sink 64 and thus the lightassembly 42 and light source 46. The cooling device 62 is utilized inconjunction with the thermal sensor 60 in controlling temperature of thelight source 46, when temperature of the light source 46 is above theminimum temperature limit. The minimum temperature limit refers to aminimum temperature as to when the cooling device 62 may be activated.

Although, the cooling device 62 may be in the form of a cooling fan, asshown, the cooling device 62 may be in some other form known in the art.The cooling device 62 may, for example, be in the form of anair-conditioning system or be in the form of a refrigeration type systemor circuit having a refrigerant contained therein. As another example,the cooling device 62 may be as simple as an air vent allowing air tocirculate and cool the light assembly 42.

The heater 63 may be external to the light source housing 48, as shown,or may be contained within the light source housing 48. The heater 63 isutilized in conjunction with the thermal sensor 60 in controllingtemperature of the light source 46, during cold starts of the vehicle 14or when temperature of the light source 46 is below the maximumtemperature limit. The maximum temperature limit refers to a maximumtemperature for operation of the heater 63; the heater 63 may beoperated at any temperature less than or equal to the maximumtemperature limit. The heater 63 increases temperature of the lightsource 46 in response to a temperature signal generated by the thermalsensor 60.

The controller 50 may be microprocessor based such as a computer havinga central processing unit, memory (RAM and/or ROM), and associated inputand output buses. The controller 50 may be an application-specificintegrated circuit or may be formed of other logic devices known in theart. The controller 50 may be a portion of a central vehicle maincontrol unit, an interactive vehicle dynamics module, a restraintscontrol module, a main safety controller, may be combined into a singleintegrated controller, a control circuit having a power supply, or maybe a stand-alone controller as shown.

The heat sink 64 may be of various size, type, and style known in theart. The heat sink 64 includes a thermal coupler layer 80 that covers aforward surface 82 of the heat sink 64 that resides between the heatsink 64 and the light source 46. The thermal coupler layer 80 providesan efficient thermal transport between the light source 46 and the heatsink 64. The thermal coupler layer 80 may be formed of indium, graphite,or of some other material having similar thermal properties.

By having the thermal system 11 within the illumination system 16,temperature of the light source 46 may be controlled without adjustingtemperature within the interior cabin 12.

Referring now to FIG. 4, a block diagrammatic view of a receiver system18 in accordance with an embodiment of the present invention is shown.The receiver system 18 includes a receiver assembly 90 having a receiver92, a filter 94, a lens 96, and a receiver system controller 98.

The receiver 92 may be in the form of a charge-coupled device (CCD)camera or a complementary metal oxide semiconductor (CMOS) camera. A CCDcamera, Model No. Wat902HS manufactured from Watec America Corporationof Las Vegas, Nev. may, for example, be used as the receiver 92. Nearinfrared light reflected off objects is received by the receiver 92 togenerate an image signal.

The filter 94 is used to filter the reflected near infrared light. Thefilter 94 may be an optical bandpass filter, which allows light within anear infrared light spectrum to be received by the receiver 92, whichmay correspond with wavelength of light contained within theillumination signal 20. The filter 94 prevents blooming caused by lightsof oncoming vehicles or objects. The filter 94 may be separate from thelens 96 and the receiver 92, as shown, or may be in the form of acoating on the lens 96 or a coating on a lens of the receiver 92, whenapplicable. The filter may be a multistack optical filter located withinthe receiver 92.

In an embodiment of the present invention, center wavelength of thefilter 94 is approximately equal to emission wavelength of the lightsource 46 and filter full-width-at-half-maximum is minimized to maximizerejection of ambient light. Also, the filter 94 is positioned betweenthe lens 96 and the receiver 92 to prevent presence of undesirable ghostor false images. When the filter 94 is positioned between the lens 96and the receiver 92 light received by the lens is incident upon thefilter 94 over a range of angles determined by the lens 96.

A filter 94A may also be positioned in front of a lens 96 rather thanbehind the lens 96 as in the case of filter 94. That is, preferably onlyone filter is employed (either 94 or 94A).

The receiver controller 98 may also be microprocessor based, be anapplication-specific integrated circuit, or be formed of other logicdevices known in the art. The receiver controller 98 may be a portion ofa central vehicle main control unit, an interactive vehicle dynamicsmodule, a restraints control module, a main safety controller, may becombined into a single integrated controller, such as with theillumination controller 50, or may be a stand-alone controller as shown.

Referring again to FIGS. 2-4, the main controller 50 controls operationof the light source 46 and the thermal control system 11 whereas thereceiver controller 98 controls operation of the receiver 92. Thecontrollers 50 and 98 may be coupled to vision system controls 100, asare shown in FIG. 2, which are mounted on a center console 102. Thesystem controls 100 may include an activation switch 104, a lightcoupler position adjuster control 106, and an illumination beambrightness control 108.

The activation switch 104 may be used to activate the vision system 10manually or the vision system 10 may be internally activated by one ofthe controllers 50 or 98. The light coupler control 106 may be coupledto a light coupler motor (not shown) for adjusting alignment angles ofthe light coupler 52 relative to the light source 46 and the optic 54.The brightness control 108 may be used for adjusting illumination beam20 intensity, which in turn adjusts indication signal brightness orclarity on the indicator 26.

The indicator 26 may include a video system, an audio system, an LED, alight, global positioning system, a heads-up display, a headlight, ataillight, a display system, a telematic system or other indicator knownin the art. The indicator 26 may indicate position, range, and travelingspeed relative to the vehicle, as well as other known object parametersor characteristics. Objects may include any animate or inanimate objectsincluding pedestrians, vehicles, road signs, lane markers, and otherobjects known in the art. In one embodiment of the present invention theindicator 26 is in the form of a heads-up display and the indicationsignal is projected to appear being forward of the vehicle 14. Theindicator 26 provides a real-time image of the target area to increasethe visibility of objects during relatively low visible light levelconditions without having to refocus ones eyes to monitor a displayscreen within the interior cabin.

Referring now to FIG. 5, a plot of transmission versus wavelength of afilter is illustrated. The dotted curve shows a typical spectrum of alaser illumination source with full width at half maximum of about 2 nm.The solid black curve shows the transmission profile of a narrowbandpass filter for the case in which its FWHM exceeds that of thelaser. As will be described below, by controlling the maximum andminimum temperature set points or by adjusting the center-wavelength ofa tunable filter, the overlap between the spectral emission of the laserand the transmission-window of the filter can be maximized. In the caseof set points, the wavelength-temperature characteristic of the lasercan be used to determine the operating temperature range that willmaximize the overlap between the laser emission and filtertransmission-window. Another approach is to measure the laser heat-sinktemperature, which using the wavelength-temperature characteristicprovides information about the emission wavelength. This information canbe used to appropriately adjust the center-wavelength of a tunablefilter. The filter center-wavelength may need to be increased ordecreased as shown in FIG. 5 since the laser wavelength will alsoincrease or decrease as the temperature changes. This will be furtherdescribed below.

Referring now to FIG. 6, a logic flow diagram illustrating a method ofthermally controlling operating range of the light source 46 inaccordance with an embodiment of the present invention is shown.

In step 146, the wavelength-temperature characteristic or curve of thelight source is obtained. The wavelength-characteristic of the lightsource may be obtained from the manufacturer. In fact, suchcharacteristics are typically provided by the manufacturer of the lightsource. If this characteristic or curve is not provided, thecharacteristic may be easily determined in a laboratory-type situation.

In step 148, a maximum and minimum temperature limit may be determinedin response to the wavelength-temperature characteristic. The maximumand minimum temperature characteristics will thus vary with respect tothe particular light source. Determining the maximum and minimum limits,the wavelength of the light source may be accurately controlled and thusthe filter may be provided having a narrow bandwidth of preferably lessthan 5 nm, more preferably between 5 and 2 nm, and even more preferablyabout 2 nm or less.

In step 150, the thermal sensor 60 generates a light source temperaturesignal in response to temperature of the light source 46.

In step 152, the controller 50 adjusts temperature of the light source46 in response to the light source temperature signal.

In step 152A, the controller 50 compares temperature of the light sourcewith the maximum temperature limit and the minimum temperature limitdetermined in step 148.

In step 152B, when the temperature of the light source 46 is less thanor equal to the maximum temperature limit, the controller 50 activatesthe heater 63 to increase temperature of the light source 46. Themaximum temperature limit using the above sample temperature range of40°-55° C., may be approximately equal to a temperature range between40°-42° C. The temperature range between 40°-42° C. may be referred toas a heater deactivation zone. The heater 63 may be activated toincrease temperature of the light source 46 even when the vision system10 is deactivated. By warming the light source 46 before activation ofthe vision system 10, light source 46 is ready for operation when thevision system 10 is activated, without time delay for ramping uptemperature of the light source 46.

In step 15, when the temperature of the light source 46 is greater thanor equal to the minimum temperature limit the controller 50 activatesthe cooling device 62 to draw thermal energy out and away from the lightsource 46, in effect cooling the light source 46. For example, the lightsource 46 may have a preferred operating temperature range ofapproximately between 40°-55° C., a minimum temperature limit may referto a temperature in a portion of that temperature range approximatelybetween 52°-55° C., depending upon thermal response time of the system10. The temperature range between 52°-55° C. may be referred to as acooling device activation zone. Of course, the ranges may vary basedupon the wavelength-temperature characteristic for each light source.

In step 152D, when the temperature of the light source is between themaximum temperature limit and the minimum temperature limit thecontroller 50 deactivated the heater 63 and the cooling device 62.

When temperature of the light source 46 is greater than or equal to anupper end of the heater deactivation zone the heater 63 is deactivated.For example, the heater deactivation zone may be approximately equal to40°-42° C., wherein the heater 63 may be deactivated; the upper end maybe approximately equal to 42° C.

When temperature of the light source 46 is less than or equal to a lowerend of the cooling device activation zone the cooling device 62 isdeactivated. For example, the cooling device activation zone may beapproximately equal to 52°-55° C., wherein the cooling device 62 may beactivated; the lower end may be approximately equal to 52° C.

The above-stated temperatures and temperature ranges, are providedsimply for example purposes only and may be adjusted depending upon theapplication. For example, in another embodiment of the present inventionthe light source 46 is maintained within an approximate temperatureoperating range of 35°-55° C.

The present invention maximizes light passage through the filter 94 bymaintaining the temperature-operating range of the light source thusmaintaining the wavelength-operating range of the light source. Bymaintaining the wavelength operating range of the light source 46, thepresent invention minimizes deviations from a filter center wavelength,which can result in reduction of light passing through the filter 94.

The controller 50 in determining operating speeds of the cooling device62 and thermal output of the heater 63 may use one or more look-uptables containing associated values corresponding to possible lightsource temperatures.

The controller 50 may ramp up or down rotational speed or thermal outputof the cooling device 62 and the heater 63, respectively, uponactivation or deactivation thereof. The controller 50 may operate thecooling device 62 and the heater 63 at incremental speeds and thermaloutputs or may gradually vary speed and thermal output thereof inresponse to changes in temperature of the light source 46.

The controller 50, in order to provide increased service life of thecooling device 62, may also adjust the cycle time of the cooling device62. For example, the cooling device 62 may provide an equivalent amountof cooling by operating the cooling device 62 at a lower speed and for alonger duration as opposed to operating the cooling device 62 at ahigher speed and for a shorter duration. In so doing, the presentinvention minimizes cycle time, or the number of times the coolingdevice 62 is activated and deactivated within a given period of time.

The controller 50 may determine in certain instances to activate thecooling device 62 or the heater 63 at a maximum speed or maximum thermaloutput, respectively, in order to provide a maximum amount of cooling orheating. For example, when temperature of the light source 46 increasesquickly over a short duration of time the controller 50 may activate thecooling device 62 at a maximum speed to rapidly cool the light source46. The controller 50 may deactivate the light source 46 when thethermal control system 11 is operating inappropriately to protect thelight source 46. When the light source 46 is deactivated the controller50 may signal a vehicle operator an alarm signal, via the indicator 26.

The above-described steps are meant to be illustrative examples; thesteps may be performed sequentially, synchronously, simultaneously, orin a different order depending upon the application.

The present invention provides a thermal control system for a lightsource of a vision system. The present invention accurately maintainstemperature of the light source and thereby also maintains accuratewavelength operating range of the light source. The present inventioncompensates for changes in ambient temperature of air proximate to thelight source in maintaining the wavelength operating range. The presentinvention minimizes the interior cabin noise caused by the cooling fan,yet provides efficient cooling of the light source.

Compared to the parent application, the present invention allows thewavelength to be maintained within about 2-3 nm of the filter centerwavelength rather than in the relatively wide range of about 15 nm.

Referring now to FIG. 7, a laser module 200 is illustrated coupled to acamera controller/tunable filter 202. The camera controller or tunablefilter may also be coupled to a direction determination detector 204. Inthis embodiment, a tunable filter such as those that have been developedin the telecommunications industry may be tuned by changing itstemperature. The tunable filter has an FWHM of several nanometers and iscomparable to the laser spectral width. The laser wavelength may bemeasured using a spectrum analyzer constructed from a tunable-filterelement or inferred from a measurement of the laser heat sinktemperature. The laser heat sink temperature as described above may bedetermined for each of the light sources used in production. Thecontroller may adjust the center wavelength of the tunable filterelement. The controller adjusts the center wavelength of the tunablefilter such that it matches the center laser wavelength. Thus, as thetemperature varies, the tunable filter may be controlled by a heater 206or other means to maintain the tunable filter center wavelength at thedesired location.

A heater or other temperature control device 208 may also be coupled tothe laser module or the laser heat sink. If a heater were included in alaser heat sink, a tunable filter-based system would also allowdeliberate tuning of the laser to enable glare-free operation ofopposing night vision systems. The direction determination detector 204may provide a signal corresponding to a direction of the vehicle such asnorth, south, east, west or those in between, to the camera controllerand the heaters 206, 208. Based upon the direction of the vehicle, thewavelengths may be tuned. For example, northbound vehicles may bepermitted to operate within a certain wavelength band and southboundvehicles assigned another wavelength band that is shifted from thenorthbound band by an amount greater than the laser spectral width.Likewise, east and westbound vehicles may also be shifted. In fact, manydifferent non-overlapping shifts may be provided for differentdirections of vehicles. For example, shifts for north, south, east, andwestbound vehicles may all be different based upon the output of thedirection determination detector 204.

In operation of this embodiment, the laser wavelength may be measureddirectly or indirectly using a spectral analyzer or inferred from theheat sink temperature. The control module may adjust the temperature orother control means for the tunable filter to move the tunable filtercenter wavelength (to longer or shorter wavelengths) to align with thecenter wavelength of the laser. In another strategy, both the lasercenter wavelength and the filter center wavelength may be adjusted bycontrolling the temperature thereon to provide a shift for vehiclesheading in different directions. The shift will allow vehicles travelingin different directions to prevent interference of the transmittingbeams with the receivers of opposing vehicles.

While the invention has been described in connection with one or moreembodiments, it is to be understood that the specific mechanisms andtechniques which have been described are merely illustrative of theprinciples of the invention, numerous modifications may be made to themethods and apparatus described without departing from the spirit andscope of the invention as defined by the appended claims.

1. A vision system of a vehicle comprising: an illuminator assembly having a light source and generating an illumination beam with a first center wavelength; an adjustable filter having an adjustable second center wavelength; a controller coupled to the filter and controlling generation of said illumination beam and controlling second center wavelength of the filter in response to the center wavelength of the light source.
 2. A vision system as recited in claim 1 further comprising a temperature controller controlling the temperature of the light source to shift the first center frequency.
 3. A vision system as recited in claim 1 wherein the controller and temperature control shift the first center frequency and second center frequency in response to vehicle direction. 